Hallucigenia, not hallucination: Scientists created 3D model of 500-mln-year-old worm

This handout picture released by Nature - University of Cambridge on June 24, 2015 shows the fossil of a prehistoric worm, the Hallucigenia sparsa, from the Burgess Shale, measuring 15 mm long. (AFP Photo / Nature - University Of Cambridge / Martin R. Smith) / AFP

Hallucigenia, a worm which inhabited oceans 500 million years ago, was discovered decades ago but there were a number of questions about its appearance and place in the tree of life. Finally scientists have put the pieces together.

A team of two researchers from Canada and Great Britain claims
that they managed to understand how hallucigenia, a 500 million
year worm, looked like. The study was published in “Nature” on
Wednesday.

Hallucigenia had seven pairs of clawed legs, seven pairs of
spines on the back over legs and six tentacles on the neck. Such
strange appearance is actually a reason why this animal got a
name “hallucigenia” – it really looks like a hallucination.

"When it was formally described originally, it was actually
upside down, with the spikes being mistaken for legs and the legs
being mistaken for tentacles on the back," Martin Smith of
the University of Cambridge, one of the authors of the study,
told the Washington Post. "Even once we got the right way up,
there was a lot of uncertainty about which end was the head and
which was the tail," he added.

Some scientists considered a bloated orb at one end of
hallucigenia as a head but the new study revealed that this
structure was just a result of animal’s decomposition. So, the
head was at the other end of its body.

"We were very optimistic, we thought we might see a pair of
eyes," Smith said. "But we didn't just see eyes. We saw
a cheeky little grin, which was a complete surprise."

The scientists discovered that hallucigenia had a mouth with a
ring of teeth which are thought to have been used for suction.
This creature also had needle-like teeth in its throat which kept
prey from sliding back out mid-slurp.

Last year the same team of researchers published another study
about hallucigenia where they placed this animal on the tree of
life. They found that its legs are similar to those of the velvet
worms, meaning that which means that hallucigenia is an ancient
member of the so-called Ecdysozoa group that embraces all molting
animals – from tiny waterbears to lobsters.

The discovery of teeth, however, prompted new questions about the
place of hallucigenia in a tree of life: modern velvet worms do
not have them. The scientists explained that from their point of
view the ultimate ancestor of all molting animals had teeth which
were reduced during the evolution process.

"These teeth resemble those we see in many early moulting
animals, suggesting that a tooth-lined throat was present in a
common ancestor," said one of the study’s authors,
Jean-Bernard Caron of the Royal Ontario Museum.